A Scientific Review of the Atkins Diet and How the Low-Carb Plan Works

On the Atkins Diet, you'll need to cut your carb intake and fuel up with nonstarchy veggies, like asparagus, and higher-fat foods, such as meat.

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The new Atkins Diet plans are not your father’s Atkins — the all-the-meat-and-fat-you-can-eat fest that gained popularity in the early 2000s.

Today, the diet, also called the Atkins Nutritional Approach, comes in two versions: Atkins 20, which is for people who want to lose more than 40 pounds (lb), who have a waist circumference of over 35 inches (women) or 40 inches (men), or who have prediabetes or type 2 diabetes; and Atkins 40, which is a plan for people who want to lose fewer than 40 lbs or who require a diet with a wider variety of foods (such as pregnant or breastfeeding women).

Though different from the original, the eating plan as a whole is still just as popular, with celebrities such as reality TV star Kim Kardashian touting its benefits for weight loss.

What Is the Atkins Diet Exactly, and How Many Carbs Can You Eat During the Program?

Both forms of the Atkins diet are focused on restricting what’s called net carbs (including those in veggies) and emphasize eating protein and healthy types of fat. Select carbs are added back to your diet as you start approaching your weight-loss goal.

Atkins defines net carbs as grams of carbs minus grams of fiber and grams of sugar alcohols. (Note that the Food and Drug Administration does not recognize "net carbs" as an accepted nutritional term.) (1)

The main difference between the various phases of the two Atkins programs is that in Atkins 20, your initial, “induction” phase limits you to 20 grams (g) of net carbohydrates, while in Atkins 40, your initial, induction phase limits you to 40 g of net carbohydrates, which gives you a little more flexibility in the foods you can eat in the beginning (including, for example, select fruits), the Atkins website notes. (2) In Atkins 20, you add net carbs back to your diet in 5 g increments (20, 25, 30, and so on), while in Atkins 40, you add net carbs back to your diet in 10 g increments, explains Lauren Popeck, RD, of Orlando Health in Florida.

To help jump-start your weight loss on the Atkins 20, you might consume some of the following foods:

Foundation veggies, such as broccoli, spinach, bok choy, and cucumbers

Protein, like eggs, chicken, and beef

All fish, including salmon, cod, flounder, and herring

Butter and olive oil

Some cheeses, such as cheddar, goat, Swiss, and Parmesan

You can find a full, comprehensive food list for phase one of the Atkins 20 on the Atkins website. (3)

If you’re following the Atkins 40 plan, you can eat all of the above, as well as the following foods (so long as you keep net carbs under 40 g per day): (4)

The premise of the Atkins Diet is that if you count and limit carbs — the body’s usual fuel — your body will be forced to burn your fat stores for energy, thereby promoting weight loss. As with many other diets, the main idea is to stop eating foods made with refined flour and sugar. But if you’re trying to follow the Atkins 20, even carb-dense whole-grain foods are on the don’t-eat list until you reach the maintenance phase.

“Cutting out carbs can contribute to weight loss initially. However, eliminating whole food groups, such as grains, milk, yogurt, and fruit, is likely unsustainable and inadequate in nutrients,” Popeck cautions. “Fiber will certainly be lacking, as well as calcium, potassium, and other vitamins and minerals.”

How Does the Atkins Diet Work? A Look at the Plan’s 4 Phases

The first phase, induction, can last from as few as two weeks to many months, depending on your goals.

The next phase, which focuses on ongoing weight loss, allows you to gradually increase your daily carb total.

For the Atkins 20 diet, this means adding more net carbs in 5 g increments and adding variety to your diet with antioxidant-rich berries, some nuts and seeds, and more vegetables. (In the Atkins 20 plan, there are technically two phases here: phase two and phase three, with phase three starting once you’re within 10 lb of your goal weight. Both phases focus on continuing to add carbs back into your diet while you continue to lose weight.)

For the Atkins 40 diet, this means adding more carbs in 10 g increments primarily by increasing portion sizes. The diet recommends moving into this phase when you are within 10 lb of your goal weight.

More on Going Low-Carb to Lose Weight

You can keep increasing carbs on both plans until you see weight loss slow or stop. At that point, depending on how close you are to your desired weight, you can move on to weight maintenance or cut back on carbohydrates if weight loss slows too much. Because protein and fats are more filling than refined carbs, the idea is you will actually tend to eat less quantity-wise yet feel full at each stage.

The final phase, which you start when you’ve reached your goal weight and have maintained it for at least a month, is a lifetime weight-maintenance plan, keeping daily net carbs to about 80 to 100 g.

The Top Foods to Eat and Avoid on the Atkins Diet

Both plans recommend avoiding sugar and refined carbs, Popeck explains. In addition, here are some of the main foods you’ll be tasked with eating and avoiding on each plan:

Not all carbs are bad. In fact, your body needs them to function properly. But there’s a difference between complex and simple carbs — and this guide can help you make smarter choices next time a craving strikes.

Some Common Snacks You Will Find on the Atkins Diet

If you’re on the Atkins 20 plan, you could choose from snacks such as: (6)

More Advice on How to Lose Weight

What Are the Pros and Cons of Following the Atkins Diet?

Like any popular diet, there are both benefits and risks to following a restricted eating plan. Here’s a look at some of them for the Atkins diet.

Possible Pros of the Atkins Diet: Easy Portions, Lower Blood Sugar, and More

There are a handful of possible pros to following the Atkins nutritional approach.

For one, the diet is relatively easy to stick to. “For people who have a weight problem, every meal is a battle, a tremendous psychological burden. A carbohydrate-restricted diet eliminates the battle,” says Richard D. Feinman, PhD, a biochemistry professor at the State University of New York Downstate Medical Center in Brooklyn, New York, and the founder and former co-editor in chief of the journal Nutrition & Metabolism. Feinman has published scientific research on Atkins and carbohydrate-restricted diets. “Protein is the stable part of the diet — that is going to give you some control over the fight with food,” he explains.

Also, the diet is not based on portion control, which some people may view as a hurdle in popular diets. “What does portion control really mean? Self-control — and that doesn’t really have a good record,” says Feinman. “Small portions are good, but on a low-carbohydrate diet, if you are still hungry, you can eat another small portion. On a low-fat diet, if you are still hungry, you may be out of luck.”

More on Trying the Atkins Diet

Susan Kraus, RD, a clinical dietitian at the Hackensack University Medical Center in New Jersey, says the simple structure of the Atkins Diet can make it straightforward for some people to adhere to. “People feel it’s easy to follow,” she says. “You focus on a few food groups, there’s simplicity in that you don’t have to measure foods, and you’re not feeling deprived.”

Following the low-carb fad diet may also help people with type 2 diabetes who are looking for a solution to high blood sugar. “Reducing carbohydrates has a health benefit, whether or not you lose weight,” says Feinman. For example, a January 2015 review published in Nutrition shows carbohydrate restriction can help in the treatment of type 2 diabetes and metabolic syndrome. (7)

Possible Cons of the Atkins Diet: Nutritional Deficiencies and a Risk of Dehydration

On the flip side, you’re not getting a well-balanced diet with the Atkins Nutritional Approach. “With any diet that eliminates a whole food group, you’re not going to get all your nutrients,” says Barbara Schmidt, RD, a lifestyle specialist at Norwalk Hospital and a nutritionist in private practice in New Canaan, Connecticut.

Then there’s the lack of fiber, an important nutrient that can help you feel full and curb unhealthy cravings. “Omitting all these food groups — [such as] grains and fruit — even if you make up nutrients with a vitamin and mineral supplement, you’re not getting enough fiber,” Kraus says. “There are also many phytochemicals, which are compounds found naturally in fruits and veggies that provide strong antioxidant effects (and that might not be found in a general multivitamin and mineral supplement), along with fiber, calcium, and vitamin D, that would not be gotten by eating this way.”

Last, the Atkins diet may cause dehydration, which could lead to light-headedness or energy loss, according to the Atkins website. (8) Carbs hold on to water in your body, so when you don’t eat carbs, you lose a lot of water weight. This can also raise your uric acid level and cause a gout attack, increase calcium loss through urine, and overwork your kidneys and liver, says Kraus.

From Our Partner

In an article published in May 2015 in Advances in Nutrition, researchers caution that although high-protein diets may be beneficial for some people looking to lose weight, it’s important to consult your healthcare provider to make sure this approach is safe for you. (9) Some research, like a study published in the Annals of Internal Medicine, shows a high-protein diet may led to reduced kidney function in women with prior mild renal dysfunction. (10)

Weight Loss Plans Like the Atkins Diet

The Atkins Diet: Short-Term and Long-Term Effects

More on Carbohydrates

“In the short term, by following the Atkins Diet, you can see results quickly. You limit food intake because you naturally don’t feel hungry,” says Kraus. “A generally healthy person can be on it for a few months without adverse effects.” Kraus’s concern is how dieters will view food: “Drastic plans cause a warped view of how to lose weight, creating a different sense of what’s okay and what’s not okay. A dieter might be mortified to have a little pasta or slice of bread.”

On the other hand, Feinman’s take on the Atkins diet is somewhat tongue-in-cheek: “Losing weight is easy: Don’t eat. If you have to eat, don’t eat carbs; if you have to eat carbs, choose carbs that are low on the glycemic index.”

Do Low-Carb Diets Like Atkins Work for Weight Loss?

As low-carb diets have grown in popularity, researchers have conducted a number of studies to assess the diets' effectiveness and additional health effects. The Harvard School of Public Health notes that some research shows low-carb diets could help people lose weight more quickly — and maintain it — more than low-fat diets can, and that moderately low-carb diets can be heart-healthy, so long as protein and fat choices come from healthy sources. (11)

A meta-analysis published in October 2012 in the American Journal of Epidemiology looked at 23 randomized controlled trials with more than 2,500 participants. (12) The researchers found that, compared with participants on a low-fat diet, participants on a low-carb diet experienced a small but statistically significant reduction in total cholesterol and triglyceride levels, and at least similar reductions in weight, waist circumference, and other disease risk factors.

The low-carb diet works like this: When carb intake is low, the body is forced to burn fat for fuel instead, creating ketone bodies that are used for energy, Popeck explains. Ketones are by-products of metabolism, and they are produced during a process called ketosis, during which the body turns to burning fat rather than carbs — a common phenomenon in those people who follow low-carb diets, such as the Atkins Diet and the ketogenic diet.

More on the Effects of a Low-Carb Diet

But Popeck also notes that it is unclear whether such diets work in the long run. “I believe low-carb diets may be nutritionally unbalanced and difficult to maintain,” she says. “I work with many patients in my clinic who have tried the Atkins Diet and successfully lost weight, but then [they] regain the lost weight and in turn have a difficult time losing weight again.“

That’s why she doesn’t recommend them. “I don’t like to promote diets because most people view them as temporary,” she explains. “For some, a low-carb program may pave the way toward healthier choices simply by eliminating sugars, sweets, and processed foods. Overall, though, in my experience, feelings of deprivation usually lead to rebound bingeing, not permanent change.”

Instead, she says, she encourages her clients to try to think of diet planning more as a lifestyle — one where all foods can fit.

Additional reporting by Stephanie Bucklin

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